In the modular link conveyor belt art, significant attention has been given to the retention of pivot rods axially in a preferred position within the bearing apertures formed in axial alignment in interdigitating modular link ends. Retention heads formed on the pivot rods have been suggested with either detenting structure for retention of preformed heads or with the formation of heads after rods are in place. It is preferable from a cost standpoint to avoid headed pivot rods. Even more important, in the repair of conveyor belts and in the maintenance it is often desirable to remove rods to uncouple belts and/or to replace worn pivot rods, and this is rarely convenient with headed rods. Thus, it has been proposed heretofore that headless pivot rods be used with retention means that permits removal and replacement.
Typically, the assignee of this invention, is co-pending U.S. applications Ser. No. 07/586,389, Sept. 20, 1990 of James M. Lapeyre now U.S. Pat. No. 5,058,732 and Ser. No. 07/610,751, Nov. 8, 1990 of Paul Horton has new U.S. Pat. No. 5,083,660 proposed retention of pivot rods in plastic belt modules by means of flexibly movable retention tabs interfering in normal position with the exit of the pivot rods from the link end apertures. These flexible tabs have the disadvantage of the possibility of breaking off with catastrophic failure in the presence of excessive force or displacement or possible conditions encountered in use of the belts.
U.S. Pat. No. 4,858,753, W. G. Hodlewsky, Aug. 22, 1989 also addresses the problem of holding headless pivot rods in position with different embodiments disclosed. Thus, in one embodiment a spring biased plug is placed in a pivot rod aperture at the edge of a link or belt to confine the pivot rod in place. This presents the significant disadvantage that extra parts must be manufactured, stored and handled in belt assembly. Thus, a second embodiment was proposed that provided for elongated pivot rod slots aligned at the slack no-load belt end with a link or belt edge pivot rod entry-exit aperture, based upon the premise that in the tension loaded belt working position, the aperture would be non-aligned and thus occlude axial displacement of a headless pivot rod.
However, this structure does not produce a fail-safe condition without problems encountered under actual belt working conditions. The belt does not always stay in a tension condition when working. For example, when heavy loads are removed, the belt may encounter slack so that the rods are temporarily moved into a position to exit the belt edge aperture. Also when belts are curved around a bend, the rods may be moved to a position for escape from the belt edgd aperture. Escape may be encouraged by various forces bearing upon the rod to flex it, to expand or contract it, etc. Also with wear of the rod the aperture tolerances change so that the rods may not be securely retained.
It is thus an object of this invention to provide improved modular link conveyor belts for axially retaining removable pivot rods securely in residence working position.